Wash and dry your new diapers before you use them. The chemicals that the fabric makers use on the cloth needs to be washed off before the diapers can be as absorbent as they are meant to be. The unbleached diapers in particular need to be washed in very hot water. You may need to turn up the water heater back up for this load if you have turned it down for safety.
Then make sure that all of the diaper is inside of the diaper cover. Also, if your baby is wearing a onesie, find out if the onesie is creeping up and coming in contact with the cloth part of the diaper.
Then check the fit of the cover. If there are big gaps at the legs or waist, you may need a smaller cover. If you buy a bigger cover hoping to save money, you may end up spending a lot of your time washing everything that your baby has on! Also, if a velcro cover is too big the diaper may end up sagging and that could cause leaks. For a really active toddler, a cover with some mesh lining can hold the diaper in place better. You may want to try pins or the Snappi fastener.
If the diaper and cover are totally saturated, you will either need to change diapers more frequently, or you will need to increase the absorbency of the diaper by doubling, by using washable liners or by using a more absorbent diaper. If you have been using fabric softeners or pure soap (ivory snow) - stop! These products actually decrease the absorbency of the diapers, making them waterproof!

Diapers need an occasional stripping if they seem to repel moisture instead of absorbing. For top loading washers - Fill your washer with warm water, add your diapers and a couple drops of plain Dawn hand dishwashing liquid. Agitate the diapers a bit while you watch. Add another drop or two and agitate while you watch. Only add enough Dawn to get a nice layer of bubbles on top - you can create an overflow in your washer if you add too much so it is important to watch for the first few minutes. Complete the wash cycle and rinse until there are no more bubbles. Dry as usual. For front loaders - You are probably going to have a suds lock if you use Dawn in your washer. I recommend washing your diapers as normal and then doing a hand wash in warm water in the tub with some Dawn. Get most of the suds out and you should be able to use your washer to rinse out the rest. Dry as usual.